Meter Bus Application ANALOG-BOARD Revision 5.1 November 1995 Revision 5.1
Dear Customer, Texas Instruments would like to thank you for your request for the ANALOG BOARD Revision 5.1 design kits. The following disclaimer applies to these design kits. In compliance with the EMC Directive (Council Directive of 3 May 1989 on the approximation of the laws of the Members States relating to electromagnetic compability (89/336/EEC) and the German Act: "Notification of the Amended Electromagnetic Compatibility Act of 30. August 1995" (para. 5 sec. 5 EMVG) the design kits you ordered have not been CE marked. The target users of these design kits are NOT end users, but exclusively professionals (ie. designers, application engineers, etc.), who are proficient in EMC matters. The design kits are intended for development only. Again, Texas Instruments would like to thank you for your request. If you have any questions, please contact your local Texas Instruments Field Sales Representative or one of your factory representatives. Sincerly Texas Instruments January 1997 2
IMPORTANT NOTICE Texas Instruments (TI) reserves the right to make changes to its products or to discontinue any semiconductor product or service without notice, and advises its customers to obtain the latest version of relevant information to verify, before placing orders, that the information being relied on is current. TI warrants performance of its semiconductor products and related software to the specifications applicable at the time of sale in accordance with TI s standard warranty. Testing and other quality control techniques are utilized to the extent TI deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed, except those mandated by government requirements. Certain applications using semiconductor products may involve potential risks of death, personal injury, or severe property or environmental damage ( Critical Applications ). TI SEMICONDUCTOR PRODUCTS ARE NOT DESIGNED, INTENDED, AUTHORIZED, OR WARRANTED TO BE SUITABLE FOR USE IN LIFE-SUPPORT APPLICATIONS, DEVICES OR SYSTEMS OR OTHER CRITICAL APPLICATIONS. Inclusion of TI products in such applications is understood to be fully at the risk of the customer. Use of TI products in such applications requires the written approval of an appropriate TI officer. Questions concerning potential risk applications should be directed to TI through a local SC sales office. In order to minimize risks associated with the customer s applications, adequate design and operating safeguards should be provided by the customer to minimize inherent or procedural hazards. TI assumes no liability for applications assistance, customer product design, software performance, or infringement of patents or services described herein. Nor does TI warrant or represent that any license, either express or implied, is granted under any patent right, copyright, mask work right, or other intellectual property right of TI covering or relating to any combination, machine, or process in which such semiconductor products or services might be or are used. Copyright 1995, Texas Instruments Incorporated 3
Table of Contents 1. Introduction... 5 2. Specification... 6 3. Description of Operation... 7 4. Circuit Description... 8 4.1 Voltage Supply... 8 4.2 Transmitter... 9 4.3 Receiver... 11 4.4 Overload Warning... 12 4.5 Repeater... 13 5. METER-BUS Application... 14 5.1 PCB: METER-BUS Interface... 15 5.2 Protection... 16 6. Appendix A - Transmission Wave Forms... 17 7. Appendix B - Parts List... 18 4
1. Introduction Electronic utility meters are becoming commonplace for measuring the consumption of electricity, water, gas and other forms of energy. The reading of such meters by personnel is unacceptably inconvenient and costly. This has stimulated the development of a remote bi-directional link between users and a central unit; such a system offers the possibility of near-continuous measurement, allows the supplier to change tariffs and to connect or disconnect users. The METER-BUS meets existing and anticipated future requirements for such a system, and has achieved widespread acceptance and standardisation. Texas Instruments has developed a special bus driver and receiver for METER-BUS user meters (slaves), the TSS721 Transceiver. This IC is powered via the METER-BUS, so that no local battery or PSU is necessary. It also does not take power from any test or measurement equipment. A corresponding analog board has been developed for the central unit. To ensure compatibility, this analog board has been conceived such that the TSS721 can be powered with 42 V. This applications proposal is concerned primarily with the analog part of the central unit; only the basic functions of the PC interface are explained. Warning: This equipment is intended for use in a laboratory test environment only. It generates, uses and can radiate radio frequency energy and has not been tested for compliance with the limits of computing devices pursuant to subpart J of 15 of FCC rules, which are designed to provide reasonable protection against radio frequency interference. Operation of this equipment in other environments may cause interference with radio communications, in which case the user at his own expense will be required to take whatever measures may be required to correct this interference. 5
2. Specification The specification (extract) is based on the DIN Proposal "Physical Layer der busfaehigen Schnittstelle", which resulted from the meeting of the working group SWG 1, CEN/SPA 176, WG 4, on 18.06.90. Parameter min typ max Unit *Number of slaves @ 1000 m 255 *Number of slaves @ 4000 m 64 Capacitance of slaves 1 nf Master to Slave **MARK 24 36 V direction SPACE MARK-12 Volt V SlavetoMaster MARK 0 1.5 ma direction SPACE 11 20 ma ***Baud rate 300 2400 baud Isolation resistance 1 MOhm Notes: * Using standard cable, for example Y-(St)Y... 2 0.8 mm. The number of slaves, on this development board, is limited up to output current of 150 ma. ** The voltage MARK max = 42 V *** The ANALOG -BOARD features communication up to 9600 baud. 6
3. Description of Operation As part of the Master, the analog board is provided with the following functions: Bus voltage modulation (TRANSMITTER) when transferring data from Master to Slave Bus current detection (RECEIVER) when transferring data from Slave to Master Powering of the bus Remote powering of slaves (via TSS721) Bus current detection on overload (OVERLOAD WARNING) System enlargement (REPEATER) Voltage regulation (VOLTAGE SUPPLY) Terminal connector (RS232 DRIVER) BUS -BUS METER - BUS BUS -BUS J3 TRANSMITTER B0 B1 B2 TX2 RECEIVER U1 Vcc RX1 B2 Vcc B0 RX1 TX1 TX2 Vcc RX1 TX1 REPEATER RS232 DRIVER BR0 J4 BR1 RxD TxD J2 OVERLOAD WARNING B1 B2 Vcc U1 -BUS Vcc VOLTAGE SUPPLY U1 J1 Figure 1: Block Diagram of ANALOG BOARD 7
4. Circuit Description The individual parts of the circuit in the block diagram ( Fig. 1) will now be separately described. The supply voltage U1 ( 18 V) should be provided by an external power supply. All voltages must be isolated from earth by a high resistance, and must also must have short-circuit protection with current limiting. The auxiliary voltage VCC is derived from the supply voltage. With this arrangement a DC/DC converter can be used to convert U1 into the required -BUS = -30V. 4.1 Voltage Supply The use of the DC/DC converter IC101 simplifies the multiple powering of the METER-BUS board and converts the U1 = 18V voltage into the auxiliary voltage of -30V. The U1 = 18V supply is loaded with about 1.5A at a bus current of IBUS = 150 ma. The auxiliary voltage VCC ensures a stable working point for the amplifier input voltage. J1-1 U1 U1 C106 470µF IC102 D101 7805 1N4001 IN OUT Vcc IC101 PT4962 - OUTPUT - com INPUT C101 4.7µF C102 1µF C103 1µF R101 13K IC103 MAX232 16 VCC 1 C1 2VCC-1.5V 2 3 C1-4 C2 5 C2- -2VCC1.5V 6 11 14 10 7 12 13 C104 1µF C105 1µF RX J1-2 R102 16K 9 0V 15 8 TX -BUS RX1 TX1 1 J2 RS232 Figure 2: Supply Voltage and RS232 Connection 8
The single 5V supply RS232 driver IC103 connects the METER-BUS Master with a PC, either directly or via a MODEM. Half-duplex RS232 transmission at 300-9600 Baud is compatible with the METER-BUS. The signal TX1 controls the bus voltage modulation in the direction to the slave, and the signal RX1 is the result of the current modulation from the slave. 4.2 Transmitter The information in the direction MASTER to SLAVE is transmitted with bus voltage modulation. The modulation pulses pass from the input TX2 via the RS232 driver IC103 (see Fig. 3) or the isolating opto coupler OC502 for REPEATER operation (see Fig. 6). The modulation amplitude (Mark -12 V) is set by the resistors R204 and R205 and the Vcc voltage. The Transmitter includes the power stages for the METER-BUS. The power amplifier IC201 is configured common-mode to to ensure the matching of the voltage reference Vcc to the bus level and the low impedance of the bus. This is in order to be able to set the output (Pin 3,6) accurately to 12 V with respect to ground potential (). The use of a basic load (R208 R213 and C206) in the central unit sets the working point for the specified data rate: the influence of external capacitances (wiring, number of slaves connected) on the rate of pulse riseand fall-times can thus be kept within limits. The remaining part of the circuit establishes the bus current when transmitting data from Slave to Master, and also supplies power for remotely powered slaves. Bus current detection is only possible if the bus voltage remains constant - i.e. slow load changes must be regulated. The starting point for such regulation is the charged state of the capacitor C202. Voltage changes on the bus are detected by comparator IC202 and compensated by current source transistor T202 until the voltage across the capacitor C204 has reached the same level as C202. The operation of the regulator stage is arranged so that in an unregulated state the resistor R208 is not conducting current. The time constants are chosen such that during data modulation (fast pulses) the slow regulation does not follow bus voltage changes. 9
U1 U1 Vcc R203 10K IC201 TLE2301 2 7 14 1 11-12 10 13 15 C201 47pF 16 3,6 4 5 8 9 R205 B0 R208 27 T202 TIP117 R209 12 C203 47µF R213 1 R214 6.8K R215 220 B1 BUS J3-1 B2 TX2 R201 10K T201 BC183 R204 10K 15K D201 1N4448 R206 2.74K D202 1N4448 R210 2.74K R212 62K C205 1µF IC202 TLE2021 2-7 6 C206 220nF R202 12K R207 249K C202 1µF R211 249K C204 22µF 3 4 -BUS -BUS J3-2 Figure 3: Transmitter The function of the resistors R208 and R213 is explained in the sections RECEIVER and OVERLOAD WARNING. 10
4.3 Receiver The receiver (see Fig. 4) detects the current pulses when data is transmitted from Slave to Master. The current sink in the slave results in a voltage drop at the terminating resistors R208 R213 (Transmitter). Vcc B2 R301 4.7K D302 BAT41 R302 4.7K R303 1.5M C301 39pF IC301 LM393/A 3 2 - C302 1µF 1 R304 680 D301 1N4148 RX1 Figure 4: Circuit Diagram of Receiver The Schottky diode D302 together with the resistors R302 and R303 sets the switching threshold, which remains stored in the capacitor C302 as a result of the long time constant. When the comparator IC301 (/A) detects a smaller voltage it recovers the signal which has been recognised. The output RX1 is supplied from the bus voltage B0 via opto coupler OC501. 11
4.4 Overload Warning This part of the circuit is necessary to indicate faults as follows: Short circuit between both bus lines Excessive load (too many slaves) on the bus U1 Vcc D401 red B2 B1 R401 39K R402 2.2K R403 12K C402 150pF IC301 LM393/B 5 6-8 4 7 R405 680 C401 10µF R404 1M C403 10µF Figure 5: Overload Warning If the voltage drop over the 1 Ohm resistor R213 (TRANSMITTER) is greater than that over the resistor R403 then the comparator IC301 switches the LED D401 on. 12
4.5 Repeater The repeater increases the distance between the Master and last Slave and also the slave loading. The transceiver TSS721 loads the Master equivalent to one slave. The opto-couplers OC1 and OC2 isolate the Repeater from the Master Analog Board. J4-1 J4-2 BR0 BR1 B0 R502 220 R503 220 IC501 TSS721 16 2 1 BUSL1 VB BUSL2 D502 5 PF 1N 10 VS 4148 11 VDD 9 BAT RIS SC RIDD STC 14 6 15 4 3 12 RX 13 RXI 8 TX 7 TXI 7 6 5 8 2 3 OC501 6N136 OC502 6N139 3 8 6 R510 620 R511 10K R512 10K C504 220pF R514 10K D501 1N4148 RX1 Vcc TX1 TX2 R516 330K C501 100nF R501 R504 120 12K C502 100nF R505 2.2K C503 10µF R506 150K R508 10K R507 15K R 2 T501 BC183 7 5 R509 10K R513 100K T502 BC183 R515 1K Figure 6: Repeater Support 13
5. METER-BUS Application This application proposal is based on the use of a PC with an RS232 termination. It supports the development, functional test and direct operation of small to medium sized test requirements. The following diagram shows the principle of a Master-Slave configuration. In a building, a telephone line is laid between the central unit and connection sockets, to which the slaves are in turn connected. The master is connected to a PC, either directly or via a MODEM. SLAVE #1 TSS721 METER - BUS SLAVE #n TSS721 18V SAFETY DEVICE Meter-Bus Analog Board Rev. 5.1 e.g. PC MODEM RS232 TELECOM MODEM Figure 7: Block Diagram Meter-Bus Master 14
5.1 PCB: METER-BUS Interface All the circuits in Figs 2 6 are on a single circuit board with dimensions of 160 100 mm. The connectors on the boards are as follows: - J1: Supply Voltage - J2: RS232 connection - J3: METER-BUS connection - J4: Repeater connection 18V J1 J3 METER - BUS J4 REPEATER DC/DC J2 RS232 Meter-Bus Analog Board Rev. 5.1 Figure 8: PCB: Meter-Bus Interface 15
5.2 Protection Various alternatives exist to protect the system against excess voltages, which could otherwise cause faulty operation or damage. Fig. 10 shows a simple approach using transient suppressor SD1 and a capacitor C1. The best solution depends very much on the application and environment, and is therefore left to the user, e.g. a short in the bus wiring blows the fuse F1. The RF emission can be reduced by connecting the cable shield to the virtual ground B. BUS F1 BUS' from Analog - Board SD1 C1 R1 B to Meter -Bus R2 -BUS -BUS Figure 10: Simple Protection Circuit 16
6. Appendix A - Transmission Wave Forms BUS RX -BUS Figure 10: Direction: MASTER TO SLAVE BUS TX -BUS Figure 11: Direction: SLAVE TO MASTER 17
7. Appendix B - Parts List PCB (Fig 7): Position Component Type Qty Notes PCB 160 x 100 mm 1 Stand height 6 mm 4 screw M3 4 Reference Voltage (Fig 2): Position Component Type Qty Notes C101 Capacitor 4.7 µf 16 V 1 Tantalum C102, Capacitor 1 µf 16 V 4 Tantalum C103, C104, C105 C106 Capacitor 470 µf 25 V 1 Elco R101 Resistor 0.25 W 13 K 5% R102 Resistor 0.25 W 16 K 5% D101 Diode 1N4001 1 IC101 DC-DC- Converter PT 4962 1 9.. 18V ±15V 190 ma IC102 Voltage regulator 7805 1 TO220 IC103 RS232 MAX232 1 Transceiver J1 Terminal block WAGO 257 2 Power Supply J2 Connector 166753-3 1 Sub-D, 25-pole, female 18
Transmitter (Fig 3): Position Component Type Qty Notes R201, Resistor 0.25 W 10 K 5% 3 R203, R204 R202 Resistor 0.25 W 12 K 5% 1 R205 Resistor 0.25 W 15 K 5% 1 R206, Resistor 0.25 W 2.74 K 1% 2 R210 R207, Resistor 0.25 W 249 K 1% 2 R211 R208 Resistor 0.25 W 27 5% 1 R209 Resistor 0.25 W 12 5% 1 R212 Resistor 0.25 W 62 K 5% 1 R213 Resistor 0.25 W 1 5% 1 R214 Resistor 0.25 W 6.8 K 5% 1 R215 Resistor 0.25 W 220 5% 1 C201 Capacitor 47 pf 100V 1 Ceramic C202 Capacitor 1 µf 25V 1 Tantalum C203 Capacitor 47 µf 25V 1 Tantalum C204 Capacitor 22 µf 25V 1 Tantalum C205 Capacitor 1 µf 100V 1 MKT C206 Capacitor 220 nf 100V 1 MKT D201, Diode 1N4448 2 D202 T201 Transistor BC183 1 npn, TO92 T202 Transistor TIP117 1 pnp-darl., TO220 IC201 Amplifier TLE2301 1 TI IC202 Amplifier TLE2021 1 TI J3 Terminal block WAGO 257 2 Bus connects, female 19
Receiver (Fig 4): Position Component Type Qty Notes R301, Resistor 0.25 W 4.7 K 5% 2 R302 R303 Resistor 0.25 W 1.5 M 5% 1 R304 Resistor 0.25 W 680 5 % 1 C301 Capacitor 39 pf 100V 1 Ceramic C302 Capacitor 1 µf 25V 1 Tantalum D301 Diode 1N4148 1 D302 Diode BAT41 1 Schottky IC301 * Comparator LM393 1/2 LM393/A * Note: 2nd half of the LM393/B is used for overload warning. Overload Warning (Fig 5): Position Component Type Qty Notes R401 Resistor 0.25 W 39 K 5% 1 R402 Resistor 0.25 W 2.2K 5% 1 R403 Resistor 0.25W 12K 5% 1 R404 Resistor 0.25 W 1M 5% 1 R405 Resistor 0.25 W 680 5% 1 C401, Capacitor 10 µf 35V 2 Tantalum C403 C402 Capacitor 150 pf 100V 1 Ceramic D401 LED red 1 Overload IC301 * Comparator LM393 1/2 LM393/B 20
Repeater (Fig 6): Position Component Type Qty Notes R501 Resistor 0.25 W 120 5% 1 R502, Resistor 0.25 W 220 5% 2 Bus protection R503 R504 Resistor 0.25 W 12K 5% 1 R505 Resistor 0.25 W 2.2 K 5% 1 R506 Resistor 0.25 W 150 K 5% 1 R507 Resistor 0.25 W 15 K 5% 1 R508, Resistor 0.25 W 10 K 5% 5 R509, R511, R512, R514 R510 Resistor 0.25 W 620 5% 1 R513 Resistor 0.25 W 100K 5% 1 R515 Resistor 0.25 W 1K 5% 1 R516 Resistor 0.25 W 330K 5% 1 C501, Capacitor 100 nf 100V 2 MKT C502 C503 Capacitor 10 µf 16 V 1 Tantalum C504 Capacitor 220 pf 100V 1 MKT D501 Diode 1N4148 1 T501, Transistor BC183 2 npn, TO92 T502 IC501 Bus-Transceiver TSS721 1 TI OC501 Optocoupler 6N136 1 OC502 Optocoupler 6N139 1 J4 Terminal block WAGO 257 2 Bus connectors, female 21